A combustion chamber structure for an internal combustion engine is known in which a shallow-dish type concave portion is formed in the top face of a piston, and a conical protrusion is formed on the bottom face of the concave portion. Further, for example, in Patent Literature 1 a combustion chamber structure is disclosed that is arranged so as to be eccentric with respect to a center axis of a cylinder. In Patent Literature 1, a combustion chamber is formed so that a diameter thereof decreases in the upward directions, that is, so that a side face of the combustion chamber inclines towards the center. Further, a lip portion at an upper end that continues to the side face of the combustion chamber is subjected to a rounding process. The lip portion is formed at a lower position than the upper end face of the piston, and a tapered face is formed from the lip portion to the upper end face of the piston.